Abstract
To design and commission a head and neck (H&N) anthropomorphic phantom that the Imaging and Radiation Oncology Core Houston (IROC-H) can use to verify the quality of intensity-modulated proton therapy H&N treatments for institutions participating in National Cancer Institute-sponsored clinical trials. The phantom design was based on a generalized oropharyngeal tumor, including critical H&N structures (parotid glands and spinal cord). Radiochromic film and thermoluminescent dosimeter (TLD)-100 capsules were embedded in the phantom and used to evaluate dose delivery. A spot-scanning treatment plan with typical clinical constraints for H&N cancer was created by using the Eclipse analytic algorithm. The treatment plan was approved by a radiation oncologist and the phantom was irradiated 4 times. The measured dose distribution using a ±7%/4 mm gamma analysis (85% of pixels passing) and point doses were compared with the treatment planning system calculations. The prescribed target dose was 6 Gy (RBE) with 646.2 cGy (RBE) and 648.6 cGy (RBE) planned to the superior and inferior TLD, respectively. For point dosimetry, the average measured-to-calculated dose ratios were 0.984 and 0.986 for the superior and inferior target TLD, respectively. Dose values for the superior and inferior target TLDs were 636.1 cGy and 639.6 cGy, respectively. For the relative dose comparison, the pixel passing rates for the axial and sagittal films, respectively, were 95.5% and 94.2% for trial 1, 97.3% and 93.2% for trial 2, 93.4% and 90.0% for trial 3, and 96.2% and 92.7% for trial 4. The anthropomorphic H&N phantom was successfully designed so that TLD measured-to-calculated ratios were within IROC-H's 7% acceptance criteria, 1.6% and 1.4% lower than expected for the superior and inferior target TLDs, respectively. All trials passed the 85% pixel passing criteria established at IROC-H for the relative dose comparison performed when using a gamma index of ±7%/4 mm.
Highlights
The use of proton therapy to treat cancer has rapidly increased during the past decade; 25 proton centers are currently in operation in the United States and 11 more are in development [1]
Each proton therapy facility already has its own set of comprehensive quality assurance (QA) tests in place, the International Commission on Radiation Units and Measurements [2] recommends an independent QA program that confirms the accuracy, comparability, and consistency of proton therapy delivery between facilities, especially for multi-institution clinical trial activities
As a core support for its clinical trials, The National Cancer Institute (NCI) funds various QA centers across the country to help ensure that institutions are delivering comparable and consistent doses of radiation, in an effort to minimize data uncertainty for trials that include radiation therapy
Summary
The use of proton therapy to treat cancer has rapidly increased during the past decade; 25 proton centers are currently in operation in the United States and 11 more are in development [1]. Each proton therapy facility already has its own set of comprehensive QA tests in place, the International Commission on Radiation Units and Measurements [2] recommends an independent QA program that confirms the accuracy, comparability, and consistency of proton therapy delivery between facilities, especially for multi-institution clinical trial activities. Its mission is to ensure that institutions participating in NCI-sponsored clinical trials have acceptable QA procedures and no significant systematic dosimetry inconsistencies, so that each site can be considered capable of providing quality and comparable clinical treatments for cancer patients. This is especially true for clinical trials that allow proton therapy, since it is a relatively new mainstream form of trial radiation therapy
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